This invention concerns a sheath for the needle of a hypodermic syringe.
Hypodermic syringe assemblies are usually provided with a protective sheath covering the needle for its protection until the syringe is required for use.
It is a common, though by no means universal, practice to change the needle of a syringe after filling and before administration of the injection because of a perception that the original needle may become blunted, bent or subjected to loss of needle lubricant during the filling operation, for example by insertion through the rubber cap of the vial, contaminated with a foreign substance, for example latex from such a cap or rendered unsterile, or to suit filling requirements for rapid filling of the syringe by using a large bore filling needle.
In the case of syringes with provision for retraction of the needle after use as disclosed for instance in our prior U.S. Pat. No. 5,782,804, the needle assembly tends to be specially designed for this purpose and it is not therefore practical to contemplate changing needles after filling the syringe and before administering the injection.
There are also concerns over the risks of drawing in fragments or slivers of material, e.g. glass, when the syringe is filled from for example an ampoule following breaking of a glass or other cap of the ampoule. Moreover, if the same needle is used to fill the syringe and also administer the medication, some injection fluid may be present on the outside of the needle which may be undesirable since some substances for injection can be irritating to the skin.
Further, it is often desirable to have the ability to administer an injection by either a retractable needle or by means of an intravenous means.